1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, and a fax machine that forms glossy images, and to an image forming apparatus that controls the gloss level in images recorded by an electrophotographic recording method and that forms three-dimensional images.
2. Description of the Related Art
Conventionally, there is an image forming apparatus that forms a color toner image by developing a latent image formed on a photoconductor, with the use of toner of plural colors. In the image formed by such an image forming apparatus, colors are reproduced by applying a powder type color material referred to as toner. When toner is applied, the gloss level changes. In the present application, the “gloss level” means the specular gloss (mirror gloss) as defined in patent document 1 and JIS (Japanese Industrial Standard) (JIS Z 8741) (see non-patent document 1). More specifically, in the present application, the “gloss level” refers to a “60 degree gloss level” as a typical example. Generally, the gloss level increases as the amount of applied toner increases. Meanwhile, the amount of toner adhering to an image varies depending on the location in the image for the purpose of reproducing various colors. Thus, in general, the gloss level is high in solid parts of the image, while the gloss level is low in halftone dot parts of the image. Consequently, the gloss level may be needlessly varied and the image quality may be degraded.
Patent documents 1 and 2 disclose an image forming apparatus that uses colorless and transparent clear toner in addition to four toner colors of Y (yellow), M (magenta), C (cyan), and K (black). In this image forming apparatus, the clear toner is applied such that the total amount of toner (including the four toner colors of Y, M, C, K and the clear toner) is even across the entire image. Accordingly, the gloss level can be made even across the entire image, regardless of the various colors reproduced by the color toner.
However, in the image forming apparatus disclosed in patent documents 1 and 2, although the gloss level on the surface of the image can be made even by applying clear toner, the extent of the expressed gloss is limited. Therefore, it has not been possible to express high glossiness such as that of a silver salt photograph.
Patent document 3 discloses an image forming apparatus and a fixing device having the following features. Specifically, an image formed on a recording medium with color toner is sandwiched by a belt whose surface is mirror-polished, so that the image is heated and melted. Subsequently, the image formed on the recording medium with color toner is cooled while being sandwiched by the belt. When the temperature of the toner becomes low, the belt is peeled off from the toner image. Accordingly, the mirror-like characteristic of the belt is transferred to the toner, so that a highly glossy image having photographic gloss is formed. The principle of the fixing process including heating and cooling a toner image sandwiched by a belt and then peeling off the belt is referred to as a “cooling and peeling principle”.
However, with such an image forming apparatus that increases the gloss level of images with the use of the cooling and peeling principle as disclosed in patent document 3, the following two problems have not been solved.
The first problem is relevant to the reproduction range of the gloss level. In the image forming apparatus according to patent document 3, the solid parts can have a high gloss level with the use of clear toner, regardless of the level of color reproduction. Furthermore, by using the fixing device employing the cooling and peeling principle, images of an even higher gloss level having photographic gloss can be formed. However, there is a lower limit to the gloss level, and therefore images of a low gloss level cannot be produced.
Images with highly glossy surfaces are high-quality, and are therefore typically used as expensive photographs. However, if images that primarily include characters and figures have a high gloss level, it may be difficult to read the characters/figures when irradiated by surrounding illumination. Therefore, images primarily including characters and figures preferably have a low gloss level. For this reason, there is also large demand for producing images with a low gloss level.
The second problem is relevant to the adjustment of the gloss level according to respective positions in a glossy image. When the image forming apparatus disclosed in patent document 3 is used to produce an image having the gloss level of a photograph, the entire image will have the gloss level of a photograph. It is not possible to produce low gloss level portions and high gloss level portions in the same image. There are cases where photographic images and character/figure images are included in the same image. In this case, the gloss level is preferably separately set for the respective portions. Furthermore, when an image includes a photographed image of a metal object, the metal texture can be expressed by increasing the gloss level at the metal part. In this case also, there is demand for a technology for changing the gloss level of part of an image.
Patent document 4 discloses an image forming apparatus in which an image is formed with the use of heat foaming toner instead of transparent toner, for producing printed matter with high added value such as Braille printing.
There is demand for high value added printing, such as increasing the height of particular images so that a user can feel the images by touching them, or Braille printing that requires the characters to have a height of 300 μm or more.
When images having a photographic gloss level are formed by conventional apparatuses, the entire image appears to have photographic gloss. Therefore, it is not possible to print an image including portions having a low gloss level and portions having a high gloss level without reducing the printing productivity.
In the conventional technology, when creating an image including photographs and low gloss level portions, or when creating an image including photographs and three dimensional images such as Braille characters, first, the gloss level of the entire image needs to be increased to a photographic gloss level. Subsequently, the image needs to be passed through a conventional image forming apparatus or an image forming apparatus with which three-dimensional printing can be performed. Accordingly, the printing productivity is significantly reduced.    Patent Document 1: Japanese Patent No. 3146367    Patent Document 2: Japanese Laid-Open Patent Application No. H9-200551    Patent Document 3: Japanese Laid-Open Patent Application No. 2007-163902    Patent Document 4: Japanese Laid-Open Patent Application No. 2003-091095    Non-patent document 1: JIS (Japanese Industrial Standard) “Specular glossiness—methods of Measurement” (JIS Z 8741-1997)